Breathing Flashcards
(26 cards)
where are the respiratory control centres situated?
in the brainstem (medulla and pons)
what does the medullary respiratory centre do?
directly provides output to respiratory muscles to produce contraction or relaxation
what does the pontine respiratory centre do?
modifies the output from the medullary respiratory centre to enable control of breathing to allow alteration of the length/depth of a breath etc
what does the cerebral cortex do?
cortical input can override intrinsic breathing pattern from RCCvia voluntary pathways which synapse with anterior horn cells (AHC) in the spinal cord enabling us to directly stimulate respiratory muscles
what do the hypothalamus/limbic systems do?
they alter breathing due to pain and a change in emotional state e.g. gasping with surprise, breathe more quickly if watching a scary film
what causes failure of the respiratory control centres (hypoventilation)?
brainstem CVA or tumour
raised intracranial pressure as there is an increased pressure on RCC
decreased level of consciousness
alcohol
drugs
central sleep apnoea
what do the respiratory control centres do?
provide the neural drive to breathe
what are effectors and what do they do?
the respiratory muscles that alter thoracic dimension to generate negative intrapulmonary pressure and therefore inspiratory flow
what do sensors (chcemoreceptors) do?
feedback to the RCC telling them when we have breathed enough
what causes the effectors to fail?
neuromuscular disease can affect the action potential reaching the effectors by
directly affecting the main nerves
failure of the action potential to propagate across a NMJ
nerve supply to the muscle doesnt function
structural change in respiratory mechanics making them work at a mechanical disadvantage e.g. kyphoscoliosis
what are stretch receptors and where are they found?
they are found in the lung parenchyma and they provide the RCC with information on the depth of breathing
what are irritant receptors and where are they found?
they are found in the airway walls and they feedback to the RCC to increase tidal volume before needing to cough
what are J receptors and where are they found?
they are found around the alveoli and they are sensitive to any increased interstitial fluid around the alveoli, and feedback to the RCC to increase respiratory frequency
what are proprioceptors and where are they found?
they are found in the lower limb joints and fire on movement, feeding back to the RCC to increase tidal volume during exercise
what do chemoreceptors do?
they are the most important receptors in the control of breathing. they sample levels of arterial CO2 and O2 and if CO2 levels start to rise they feedback to RCC to stop inspiration
what are three advantages of a CO2 based ventilatory system?
CO2 production is related to O2 production
CO2 production is related to pH
CO2 has a linear relationship to ventilation
what do peripheral chemoreceptors do and where are they found?
there are two sets located in the aortic arch and carotid body
they are sensitive to arterial hypoxaemia (when PaO2 falls to 8kpa or less), increased H+ and weakly sensitive to PaCO2
what do central chemoreceptors do and where are they located?
they are responsible for 70% of the drive to breathe
they are located on the ventrolateral surface of the medulla bilaterally and are bathed in cerebral spinal fluid
they are sensitive to arterial hypercapnia (increased PaCO2), specifically increased H+ concentraition
what happens at the blood brain barrier?
CO2 diffuses into CSF and combines with water to form carbonic acid, which dissociates into bicarbonate and H+ which increases acidity, decreases pH and stimulates central chemoreceptors which feedback to RCC
what happens at RCC when the central chemoreceptors feedback?
RCC stimulates effectors, which increase rate and depth of ventilation until CO2 / pH levels are back in normal range
what does stimulation of the CCR do to the sympathetic and parasympathetic nervous systems?
increased SNS activity (increasing HR and arterial BP), inhibits PNS activity
what are the indications for oxygen therapy?
hypoxaemia (<7.8kPa)
what are the target sats for patients not at risk of hypercapnia?
94-98%
what are the target sats for patients at risk of hypercapnia?
88-92%
